1. Field of the Disclosure
The disclosure relates to curable polyureasil compounds, methods related to curing of such compounds via hydrolysis and/or condensation to form coatings on a substrate, and coated articles formed from the curable polyureasil compounds.
2. Brief Description of Related Technology
Aluminum and aluminum alloys (AA) are important materials, mainly for aerospace applications among many others. Protection of aluminum-based materials from atmospheric corrosion is important for long term durability and costs associated with their maintenance. Aircraft coatings are designed to provide long-lasting corrosion and abrasion protection in addition to decorative functions. The coating system is typically comprised of a conversion coating layer, a primer layer, and a topcoat layer.
A conversion coating is a type of coating deposited at the metal surface such that it is strongly adherent and covalently bonded to the surface, thus providing excellent adhesion and a barrier for corrosive elements. Additionally, it provides for good adhesion of the primer layer to its surface. Thus, conversion coatings (surface pretreatments) have an important role in the success of a composite coating system such as used for aircraft.
Among available technologies for surface pretreatments, chromate conversion coatings are by far the most efficient for aluminum and alloys. These coatings are typically applied from acidic mixtures of soluble hexavalent chromium salts by oxidation-reduction reactions with the metal surface. A continuous layer of insoluble trivalent chromium and soluble hexavalent chromium compounds are formed. The use of chromates in the coating has generated serious environmental and health issues for the coating industry because hexavalent chromates are carcinogenic and highly toxic [1]. The costs associated with worker safety and the containment, treatment, and disposal of hazardous materials related to the coating process is one of the highest costs for maintenance activities in the Air Force [2]. Recent legislation, however, substantially limits the use of chromate-based coatings.